During a recovery process for hydrocarbons, particularly heavy oil, the inherent high viscosity of heavy oil (HO) is an obstacle to reservoir production and subsequent handling on the surface. Thus, heating techniques, for example electromagnetic (EM) heating, may be used to reduce the viscosity of the oil. The oil may then be extracted through the borehole for onsite or offsite refinement.
EM heating is particularly useful as conventional steam injection techniques for heavy oil recovery are sometimes limited to relatively shallow, thick, and permeable reservoirs. EM heating refers to heating produced by the absorption of electromagnetic energy by the molecules in formation. EM heating does not require a heat transporting fluid such as steam, which can be beneficial for deep reservoirs and thin pay-zones. In fact, EM thermal processes are mostly free of issues such as poor heat transfer, shale layers between rich oil layers, cap rock requirement, and the difficulty of controlling the movement of injected fluid and gases, all of which have impacted other thermally stimulated recovery processes.
EM heating can be divided based on the frequency of the electrical current used by the source, direct (DC)/low frequency currents and high frequency (radio frequency, microwave) currents, which may be employed depending on reservoir fluid properties (e.g., resistivity, dielectric permittivity) and other formation characteristics.
Applications of EM heating for heavy oil recovery may benefit from detailed analysis. Previous analytical models use relatively strong assumptions and focus on a single range of frequencies (i.e., high frequency or low frequency). They consider only a single electrode (low frequency) or antenna (high frequency), and calculate the heating rate for a homogenous single layered formation where in the case of low frequency heating, approximation of infinitely long electrode and for the high frequency heating, Lambert's law of absorption as a simplified radial model of EM wave propagation have been adopted.